Most people do answer the phone when they don't recognize the number. And if you don't want people calling you, don't put your phone number on the business card you give to random people.
I instinctively disagree with the first point (and completely agree with the second, but regardless, I don't think a card with a number makes for an open invite), but then again, I don't cold call a lot of folks. The idea that someone would hand over control of their time to other random people just strikes me as strange.